The water table is often found to be a subdued form of topography. This undulating water table can result in nested (local, intermediate and regional) groundwater flow systems (Tóth, 1963). The existence of this nested groundwater flow phenomenon was largely derived from analytical and numerical solutions in which the undulating water table was treated as a fixed upper hydraulic head boundary condition. Although this phenomenon has been widely accepted, the appropriateness of using a spatially-varying hydraulic head as the top boundary condition in previous studies has not been assessed. In this study, we use the physically-based, spatially-distributed hydrological simulator HydroGeoSphere to investigate this issue. HydroGeoSphere allows us to relax boundary conditions and to simulate coupled surface water and groundwater flow. Two classic regional flow models introduced by Tóth (1963) were adapted to perform numerical simulations. Two different hydrologic regimes representing semi-arid and humid regions were employed as contrasting settings. We first ran the two models by using the hydraulic head from Tóth (1963) as the boundary condition (i.e., a pure groundwater process). The results show that extremely large, physically implausible, spatially-varying groundwater recharge fluxes are required in high-elevation areas for consistency with the hydraulic head boundary applied in the original Tóth (1963) models. These recharge fluxes exceed reasonable precipitation rates. In the second set of models, we let flow systems generate themselves naturally. We did this by simulating surface flow and groundwater flow in a fully-coupled hydrological process. The top boundary was driven by reasonable and physically-based precipitation and potential evapotranspiration. The results show an undulating water table and that nested groundwater flow develops in low-elevation areas but that a relatively flat water table and exclusively regional flow occurs at high-elevation areas. Overall, this study demonstrates the critical role boundary conditions play in the development of nested flow systems.